Structural variations involving both morphological and syntactic features of the complex sentence of the type “When S, S” and their relevance for the interpretation of sentence meaning are analyzed. It is hypothesized that the constraints on certain sequences intuitively felt by native speakers are due to semantic contradictions that arise between the indexical content of the verbal tense and aspect and the syntactic structure of the sentence which iconically reflects the cognitive processing of perceptual data. The cognitive value of different syntactically acceptable sequences is assessed from the point of view of the relationship between the morphosyntactic categories of tense and as-pect and sentence iconicity.